The invention relates to a non-recursive half-band filter. Such filters have become known from the paper by Bellanger et al, entitled, "Interpolation, Extrapolation, and Reduction of Computation Speed in Digital Filters," published in IEEE Transactions on Acoustics, Speech and Signal Processing, Vol. ASSP-22, No. 4, August, 1974, pages 231-235.
The known half-band filters process real input signals into real output signals.